/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You under the Apache License, Version 2.0
 *  (the "License"); you may not use this file except in compliance with
 *  the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */
package org.apache.tomcat.util.buf;

import java.io.CharConversionException;
import java.io.IOException;

/**
 * All URL decoding happens here. This way we can reuse, review, optimize
 * without adding complexity to the buffers.
 * <p>
 * The conversion will modify the original buffer.
 *
 * @author Costin Manolache
 */
public final class UDecoder {

	public static final boolean ALLOW_ENCODED_SLASH =
			Boolean.parseBoolean(System.getProperty("org.apache.tomcat.util.buf.UDecoder.ALLOW_ENCODED_SLASH", "false"));
	/**
	 * Unexpected end of data.
	 */
	private static final IOException EXCEPTION_EOF = new DecodeException("EOF");
	/**
	 * %xx with not-hex digit
	 */
	private static final IOException EXCEPTION_NOT_HEX_DIGIT = new DecodeException(
			"isHexDigit");
	/**
	 * %-encoded slash is forbidden in resource path
	 */
	private static final IOException EXCEPTION_SLASH = new DecodeException(
			"noSlash");

	public UDecoder() {
	}

	private static boolean isHexDigit(int c) {
		return ((c >= '0' && c <= '9') ||
				(c >= 'a' && c <= 'f') ||
				(c >= 'A' && c <= 'F'));
	}

	private static int x2c(byte b1, byte b2) {
		int digit = (b1 >= 'A') ? ((b1 & 0xDF) - 'A') + 10 :
				(b1 - '0');
		digit *= 16;
		digit += (b2 >= 'A') ? ((b2 & 0xDF) - 'A') + 10 :
				(b2 - '0');
		return digit;
	}

	private static int x2c(char b1, char b2) {
		int digit = (b1 >= 'A') ? ((b1 & 0xDF) - 'A') + 10 :
				(b1 - '0');
		digit *= 16;
		digit += (b2 >= 'A') ? ((b2 & 0xDF) - 'A') + 10 :
				(b2 - '0');
		return digit;
	}

	// -------------------- Additional methods --------------------
	// XXX What do we do about charset ????

	/**
	 * URLDecode, will modify the source.  Includes converting
	 * '+' to ' '.
	 *
	 * @deprecated Unused. Will be removed in Tomcat 8.0.x onwards.
	 */
	@Deprecated
	public void convert(ByteChunk mb)
			throws IOException {
		convert(mb, true);
	}

	/**
	 * URLDecode, will modify the source.
	 */
	public void convert(ByteChunk mb, boolean query)
			throws IOException {
		int start = mb.getOffset();
		byte buff[] = mb.getBytes();
		int end = mb.getEnd();

		int idx = ByteChunk.findByte(buff, start, end, (byte) '%');
		int idx2 = -1;
		if (query) {
			idx2 = ByteChunk.findByte(buff, start, (idx >= 0 ? idx : end), (byte) '+');
		}
		if (idx < 0 && idx2 < 0) {
			return;
		}

		// idx will be the smallest positive index ( first % or + )
		if ((idx2 >= 0 && idx2 < idx) || idx < 0) {
			idx = idx2;
		}

		final boolean noSlash = !(ALLOW_ENCODED_SLASH || query);

		for (int j = idx; j < end; j++, idx++) {
			if (buff[j] == '+' && query) {
				buff[idx] = (byte) ' ';
			} else if (buff[j] != '%') {
				buff[idx] = buff[j];
			} else {
				// read next 2 digits
				if (j + 2 >= end) {
					throw EXCEPTION_EOF;
				}
				byte b1 = buff[j + 1];
				byte b2 = buff[j + 2];
				if (!isHexDigit(b1) || !isHexDigit(b2)) {
					throw EXCEPTION_NOT_HEX_DIGIT;
				}

				j += 2;
				int res = x2c(b1, b2);
				if (noSlash && (res == '/')) {
					throw EXCEPTION_SLASH;
				}
				buff[idx] = (byte) res;
			}
		}

		mb.setEnd(idx);

		return;
	}

	/**
	 * In-buffer processing - the buffer will be modified
	 * Includes converting  '+' to ' '.
	 *
	 * @deprecated Unused. Will be removed in Tomcat 8.0.x onwards.
	 */
	@Deprecated
	public void convert(CharChunk mb)
			throws IOException {
		convert(mb, true);
	}

	/**
	 * In-buffer processing - the buffer will be modified
	 */
	public void convert(CharChunk mb, boolean query)
			throws IOException {
		//        log( "Converting a char chunk ");
		int start = mb.getOffset();
		char buff[] = mb.getBuffer();
		int cend = mb.getEnd();

		int idx = CharChunk.indexOf(buff, start, cend, '%');
		int idx2 = -1;
		if (query) {
			idx2 = CharChunk.indexOf(buff, start, (idx >= 0 ? idx : cend), '+');
		}
		if (idx < 0 && idx2 < 0) {
			return;
		}

		// idx will be the smallest positive index ( first % or + )
		if ((idx2 >= 0 && idx2 < idx) || idx < 0) {
			idx = idx2;
		}

		final boolean noSlash = !(ALLOW_ENCODED_SLASH || query);

		for (int j = idx; j < cend; j++, idx++) {
			if (buff[j] == '+' && query) {
				buff[idx] = (' ');
			} else if (buff[j] != '%') {
				buff[idx] = buff[j];
			} else {
				// read next 2 digits
				if (j + 2 >= cend) {
					// invalid
					throw EXCEPTION_EOF;
				}
				char b1 = buff[j + 1];
				char b2 = buff[j + 2];
				if (!isHexDigit(b1) || !isHexDigit(b2)) {
					throw EXCEPTION_NOT_HEX_DIGIT;
				}

				j += 2;
				int res = x2c(b1, b2);
				if (noSlash && (res == '/')) {
					throw EXCEPTION_SLASH;
				}
				buff[idx] = (char) res;
			}
		}
		mb.setEnd(idx);
	}

	// XXX Old code, needs to be replaced !!!!
	//

	/**
	 * URLDecode, will modify the source
	 * Includes converting  '+' to ' '.
	 *
	 * @deprecated Unused. Will be removed in Tomcat 8.0.x onwards.
	 */
	@Deprecated
	public void convert(MessageBytes mb)
			throws IOException {
		convert(mb, true);
	}

	/**
	 * URLDecode, will modify the source
	 */
	public void convert(MessageBytes mb, boolean query)
			throws IOException {

		switch (mb.getType()) {
			case MessageBytes.T_STR:
				String strValue = mb.toString();
				if (strValue == null) {
					return;
				}
				try {
					mb.setString(convert(strValue, query));
				} catch (RuntimeException ex) {
					throw new DecodeException(ex.getMessage());
				}
				break;
			case MessageBytes.T_CHARS:
				CharChunk charC = mb.getCharChunk();
				convert(charC, query);
				break;
			case MessageBytes.T_BYTES:
				ByteChunk bytesC = mb.getByteChunk();
				convert(bytesC, query);
				break;
		}
	}

	/**
	 * @deprecated Unused. Will be removed in Tomcat 8.0.x onwards.
	 */
	@Deprecated
	public final String convert(String str) {
		return convert(str, true);
	}

	public final String convert(String str, boolean query) {
		if (str == null) {
			return null;
		}

		if ((!query || str.indexOf('+') < 0) && str.indexOf('%') < 0) {
			return str;
		}

		final boolean noSlash = !(ALLOW_ENCODED_SLASH || query);

		StringBuilder dec = new StringBuilder();    // decoded string output
		int strPos = 0;
		int strLen = str.length();

		dec.ensureCapacity(str.length());
		while (strPos < strLen) {
			int laPos;        // lookahead position

			// look ahead to next URLencoded metacharacter, if any
			for (laPos = strPos; laPos < strLen; laPos++) {
				char laChar = str.charAt(laPos);
				if ((laChar == '+' && query) || (laChar == '%')) {
					break;
				}
			}

			// if there were non-metacharacters, copy them all as a block
			if (laPos > strPos) {
				dec.append(str.substring(strPos, laPos));
				strPos = laPos;
			}

			// shortcut out of here if we're at the end of the string
			if (strPos >= strLen) {
				break;
			}

			// process next metacharacter
			char metaChar = str.charAt(strPos);
			if (metaChar == '+') {
				dec.append(' ');
				strPos++;
				continue;
			} else if (metaChar == '%') {
				// We throw the original exception - the super will deal with
				// it
				//                try {
				char res = (char) Integer.parseInt(
						str.substring(strPos + 1, strPos + 3), 16);
				if (noSlash && (res == '/')) {
					throw new IllegalArgumentException("noSlash");
				}
				dec.append(res);
				strPos += 3;
			}
		}

		return dec.toString();
	}

	private static class DecodeException extends CharConversionException {
		private static final long serialVersionUID = 1L;

		public DecodeException(String s) {
			super(s);
		}

		@Override
		public synchronized Throwable fillInStackTrace() {
			// This class does not provide a stack trace
			return this;
		}
	}

}
